You should copy the .desktop file into the ~/.local/share/applications/ directory before editing it. Updates will overwrite changes to the files in /usr/share/applications/.
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dobeyFeb 5 '14 at 23:01

@dobey, I was thinking about that myself. But, when i edited the file the ubuntu tweak icon was still in the Control Center. It seems that the Control Center only reads the file from /usr/share/applications/? Thats what I concluded anyways.
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blade19899Feb 5 '14 at 23:07